Photographic backing paper



Nov. 18, 1941- E. L. BAXTER PHOTOGRAPHIC BACKING PAPER Filed Nov.- 2,'1940 wank? IN V EN TOR W A TTORNEYS Patented Nov. 18, 1941 PHOTOGRAPHICBACKING PAPER Ernest L. Baxter, Rochester, N. Y., assignor to EastmanKodak Company, Rochester, N. Y., a corporation of New Jersey ApplicationNovember 2, 1940, Serial No. 364,061

4 Claims.

This invention relatesto photographic backing paper, and moreparticularly to the ink with which photographic backing paper is marked.

As is well known in the art, it is customary to roll up photographicroll film with a strip of backing paper, which is usually black on oneside and colored on the other. This backing paper carries, on thecolored side, markings or indicia which can be seen through the smallwindow in the back of the camera, and indicate to the user the points atwhich winding should be stopped, and the serial numbers of theexposures. The markings are usually covered by a transparent overcoatingon the paper. When the film is rolled up with the backing paper, theprinted side of the paper is in contact with the emulsion side of thefilm.

The accompanying drawing shows a section of two convolutions of filmwith an interposed layer of backing paper, as it occurs in a roll filmcartridge. I, I represents the film base, carrying the emulsion 2, 2. 3represents the backing paper, carrying indicia 4.

The inks which have been most used for mark-- ing photographic backingpaper usually consist of a dye, a binder and a solvent, and are such asto have no effect on unexposed photographic emulsions with which theyare in contact. However, if a considerable period of time fel'apsesbetween the exposure of a portion of the film and its development, sothat the backing paper remains in contact with an emulsion containing alatent image, the markings on the backing paper may reproduce themselvesas an intensification of the latent image on the film. When the film isdeveloped, the markings thus appear in the pictures.

I have discovered that intensification of the latent image on aphotographic film by the markings on the backing paper may be preventedbyv incorporating certain reducing agents in the ink used for markingthe backing paper. I have tested a very considerable number of reducingagents for this purpose, I have found only a few which are operative.These are: sodium sulfite, ferrous sulfate, sodium formaldehydesulfoxylate, and sodium hydrosulfite. I prefer to use sodium sulfitebecause it oxidizes to sodium sulfate, which is normally found as aloading agent in all dyes and hence does not introduce a foreignsubstance into the ink.

While I have found that an amount of sodium sulfite equal to about 1% ofthe total solids in the ink is effective for preventing intensificationof the latent image by the ink. 0.5% has been found to be ineffective,and 2% has been found to destroy the latent image. 1% of sodium sulfite,based on the total solids in the ink, has been found to have no actionon unexposed film even under tropical storage conditions.

By way of illustration, by which I am not to be limited, I give thefollowing example of an ink for marking photographic backing paperaccording to my invention.

2% of Nigrosine 2011 Gone. is dissolved in a 4% aqueous gelatin solutionto form an ink. To 25 /2 lbs. of this ink is added 7 grams of sodiumsulfite dissolved in 100 cc. of hot water.

What I claim as'my invention and desire to be secured by Letters Patentof the United States is:

1. Photographic backing paper bearing indicia printed with an inkcomprising a dye and approximately l%, calculated on the total solids inthe ink, of a reducing agent selected from the group consisting ofsodium sulfite, ferrous sulfate, sodium formaldehyde sulfoxylate andsodium hydrosulfite.

2. Photographic backing paper bearing indicia printed with an inkcomprising a dye and approximately 1%, calculated on the total solids inthe ink, of sodium sulfite.

3. A roll film cartridge comprising inter-rolled strips of film carryinga photographic emulsion and of backing paper, that surface of thebacking paper which is in contact with the photographic emulsioncarrying indicia printed with an ink comprising a dye and approximately1%. calculated on the total solids in the ink, of a reducing agentselected from the group consisting of sodium sulfite, ferrous sulfate,sodium formalde hyde sulfoxylate and sodium hydrosulfite.

4. A roll film cartridge comprising inter-rolled strips of film carryinga photographic emulsion and of backing paper, that surface of thebacking lated on the total solids in the ink, of sodium ERNEST L.BAIXTER.

